Solubilization and partial purification of cholinephosphotransferase in hamster tissues

CDPcholine:1,2-diacylglycerol cholinephosphotransferase (EC 2.7.8.2) is located on the cytoplasmic side of the endoplasmic reticulum, and catalyzes the final step in the synthesis of phosphatidylcholine via the CDPcholine pathway. The enzyme was solubilized from hamster liver microsomes by 3% Triton QS-15, and partially purified by DEAE-Sepharose chromatography and Sepharose 6B chromatography. The microsomal and partially purified enzymes displayed similar pH profile, and both showed absolute requirement for Mg++ or other divalent cations. The Km values of CDPcholine were similar between microsomal and partially purified enzyme, whereas the Km value for diacylglycerol was substantially lowered when the enzyme was partially purified. Hamster heart cholinephosphotransferase was not solubilized by Triton QS-15.